Conventional handoff method is restricted within the handoff of identical systems and assumes that mobile terminals and a network are synchronized by GPS (Global Positioning System). This assumption is no longer valid because the third generation 3GPP (Global Partnership Project) DS (Direct Spreading) system works at an asynchronous mode.
To make the handoff between a mobile terminal communicating with the third generation 3GPP DS system and the second generation IS95 system, a connection with the third generation 3GPP DS system must be terminated beforehand. It is because 3GPP DS systems work on the asynchronous mode and IS95 synchronous information cannot be transmitted to the mobile terminal.
Consequently, handoff success rate drops because acquiring pilot channel of second generation IS95 system, interpreting synchronous channel message, and establishing traffic channels have to be performed and therefore mobile terminals stay in disconnected state for a relatively longtime.